No, ypu cannot delete individual items.
But you can clean sections and start anew - settings => iCloud => manage storage.
Or you can pay for additional storage.
Or: delete all iCloud storage/back ups and start fresh. SERIOUSLY: do you need everything in iCloud?
For photos and camera videos you can use dropbox, onedrive, mega etc etc etc
USE iCloud only for settings, mail, apps etc - iPhone specific stuff.
General content you can back up to any one of a few dozen free alternatives.